|
|
A035290
|
|
Number of ways to place a non-attacking white and black pawn on n X n chessboard.
|
|
2
|
|
|
0, 0, 6, 50, 194, 522, 1142, 2186, 3810, 6194, 9542, 14082, 20066, 27770, 37494, 49562, 64322, 82146, 103430, 128594, 158082, 192362, 231926, 277290, 328994, 387602, 453702, 527906, 610850, 703194, 805622, 918842, 1043586, 1180610
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,3
|
|
LINKS
|
|
|
FORMULA
|
a(n) = n^4 - 4 n^3 + n^2 + 10 n - 6.
G.f.: -2*x^3*(x+1)*(x^3-5*x^2+7*x+3)/(x-1)^5. [Colin Barker, Jan 09 2013]
|
|
EXAMPLE
|
There are 6 ways of putting 1 white and 1 black pawn on 3 X 3 so that neither can capture the other. pawns can't be on first or last rank.
|
|
MATHEMATICA
|
CoefficientList[Series[- 2 x^2 (x + 1) (x^3 - 5 x^2 + 7 x + 3)/(x - 1)^5, {x, 0, 50}], x] (* Vincenzo Librandi, Oct 20 2013 *)
|
|
PROG
|
(Magma) [n le 2 select 0 else n^4-4*n^3+n^2+10*n-6: n in [1..50]]; // Vincenzo Librandi, Oct 20 2013
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|